Rotor Yoke and Method of Making the Same

ABSTRACT

A method of making a composite rotor yoke includes preparing a molded rotor yoke in a closed cavity tool and possibly machining at least one portion of the molded rotor yoke to form the rotor yoke. In the preferred embodiment, preparing the molded rotor yoke is accomplished by applying layers of uncured low-flow composite material and a layer of uncured high-flow adhesive; substantially enclosing the uncured molded rotor yoke in the closed cavity tool; applying pressure so as to compress the uncured molded rotor yoke; and curing the uncured molded rotor yoke. During the curing process, the high-flow adhesive bleeds out of the molded rotor yoke, thereby preventing marcels from forming through movement of the low-flow composite material.

TECHNICAL FIELD

The present application relates to rotorcraft and, in particular, toyokes for coupling helicopter blades to a mast.

DESCRIPTION OF THE PRIOR ART

Each blade of the main rotor assembly of a rotorcraft must be connectedto a main support mast, usually by means of a rotor yoke, in a mannerallowing several degrees of freedom. Such an interconnection issubjected to high and repeated stresses of both torsional andcentrifugal natures, and is therefore an extremely important componentof the aircraft. Each blade must be able to rotate about itslongitudinal axis to provide pitch control. Each blade must be able toflap in a direction perpendicular to the rotor plane to accommodatevertical loads. In some instances, each blade must be able to pivotwithin the rotor plane to provide for lead-lag control. The manner inwhich the blades are secured to the main support mast enables arotorcraft to be controlled and maneuvered in flight.

Various types of rotor yokes have been utilized to interconnect therotorcraft blades and the support mast. Metal rotor yokes have sufferedfrom the disadvantages of weight, cost, high maintenance requirements,and low useful life. There have been several attempts to eliminate oneor more of the articulations in such couplings in order to simplifyconstruction and reduce costs. Some rotor yokes are pivotally secured tothe support mast, and are characterized by a flat plate constructionresilient enough to act as a virtual hinge and thereby accommodateflapping of the blades.

More recently, glass fibers and other composite materials have beenemployed in the fabrication of rotorcraft rotor system components. Incomparison to a machined metal forging, glass fibers and other compositematerials have more favorable fatigue characteristics resulting inlonger useful life. In addition, the use of such materials simplifiesconstruction and reduces costs. Referring to FIGS. 1 and 2, compositerotor yokes, such as a rotor yoke 101 are conventionally cured in arigid, closed mold, such as mold 103, to form the overall shape of therotor yoke. One of the problems encountered concerning such rotorcraftrotor yokes has been distortion or “marcelling” of the fibers in therotor yoke during the curing process. Because the uncured rotor yoke isforced to conform to the cavity, such as cavity 105 formed by the closedmold, mechanical stresses can be induced in the uncured rotor yoke. Thefibers are substantially unconstrained during certain portions of thecuring cycle when the resin matrix in which the fibers are disposed isin a semi-liquid or liquid state. The induced stress in the uncuredrotor yoke is relieved via movement or distortion of the fibers withinthe resin matrix. The fibers can be captured in their distorted ormarcelled state when the resin crosslinks in thermosetting compositematerials or when the resin is cooled in thermoplastic compositematerials.

There are many designs of rotorcraft yokes well known in the art;however, considerable shortcomings remain.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the present applicationare set forth in the appended claims. However, the system itself, aswell as a preferred mode of use, and further objectives and advantagesthereof, will best be understood by reference to the following detaileddescription when read in conjunction with the accompanying drawings, inwhich the leftmost significant digit(s) in the reference numeralsdenote(s) the first figure in which the respective reference numeralsappear, wherein:

FIGS. 1 and 2 are stylized, cross-sectional views illustrating aconventional method for manufacturing a composite rotor yoke for arotorcraft according to prior art;

FIGS. 3-5 are stylized, cross-sectional views depicting the method ofmanufacturing a composite molded rotor yoke according to the preferredembodiment of the present application;

FIGS. 6-8 are stylized, cross-sectional views depicting the method ofmanufacturing a composite molded rotor yoke according to an alternativeembodiment of the present application;

FIG. 9 is a stylized, cross-sectional view of a molded rotor yokeaccording to an alternative embodiment of the present application;

FIG. 10 is a top, plan view of a composite rotor yoke according to thepreferred embodiment of the present application; and

FIG. 11 is a top, plan view of a rotor hub incorporating a pair ofcomposite rotor yokes of FIG. 10 according to the preferred embodimentof the present application.

While the system of the present application is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the present application tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the present application as defined by theappended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The system of the present application represents a composite rotor yokefor a rotorcraft produced using a closed cavity curing tool. Preferably,the composite rotor yoke is laid-up using an automated fiber placementprocess, but may also be laid-up by hand. After curing, the curedcomposite rotor yoke may be machined to add any desired features.

Illustrative embodiments of the present application are described below.In the interest of clarity, not all features of an actual implementationare described in this specification. It will of course be appreciatedthat in the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

As used herein, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present application, the devices,members, apparatuses, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “above,” “below,”“upper,” “lower,” or other like terms to describe a spatial relationshipbetween various components or to describe the spatial orientation ofaspects of such components should be understood to describe a relativerelationship between the components or a spatial orientation of aspectsof such components, respectively, as the device described herein may beoriented in any desired direction.

Referring to FIGS. 3-5 in the drawings, the preferred embodiment of acomposite molded rotor yoke 501 of a rotor yoke 901 (shown in FIG. 10)is fabricated by applying a plurality of layers of an uncured low-flowcomposite material 503 and a layer of a high-flow adhesive 505 into aclosed cavity tool 507. Note that the geometric configuration of tool507 is merely exemplary of the widely diverse geometric configurationsof closed cavity tools contemplated by the present application. Itshould be appreciated that tools 509, 510, 511, and 512 may be splitinto multiple tools, or combined to form a fewer number of tool parts.For example, side tools 510 and 512 may be integrated into a second tool511 so as to form one integral tool part. Closed cavity tool 507preferably has a rigid first tool 509, a rigid second tool 511, andrigid side tools 510 and 512. However, closed cavity tool 507 may alsohave a semi-rigid first tool 509, a semi-rigid second tool 511,semi-rigid side tools 510 and 512, or any combination of semi-rigid andrigid tools 509, 511, 510, and 512. Closed cavity tool 507 providestolerance and contour control by conforming the primary surfaces ofmolded rotor yoke 501 to the inside surfaces of closed cavity tool 507.Closed cavity tool 507 may also be referred to as a “two-sided” tool orother language describing that tool 507 substantially encloses moldedrotor yoke 501.

Uncured, composite molded rotor yoke 501 is formed when the desirednumber of layers, also referred to as “plies”, of low-flow compositematerial 503 and high-flow adhesive 505 have been applied into tool 507,in the desired geometry. Layers of low-flow composite material may belaid by hand, or by fiber placement machine 513. High-flow adhesive 505may also be laid by hand, or by a machine similar to fiber placementmachine 513. Closed cavity tool 507 is capable of compressing moldedrotor yoke 501 into a desired thickness and geometry. Closed cavity tool507 may include stops 515 a and 515 b so that first tool 509 and secondtool 511 of tool 507 will stop the compression of molded rotor yoke 501at the desired thickness of molded rotor yoke 501. Closed cavity tool507 may also include fastener holes 517 a and 517 b so that closedcavity tool 507 could be fastened closed with fasteners 521 a and 521 bat any time during or after the curing process.

Uncured low-flow composite material 503 preferably includes glass fibersdisposed in an uncured epoxy, in the form of a prepreg, although thepresent application contemplates other materials for molded rotor yoke501. An example of low-flow composite material 503 is HexPly 8552 madeby Hexcel Composites. For this application, the term “prepreg” istypically sheets of fibers impregnated in uncured epoxy or adhesive.Uncured low-flow composite material 503 can then be cut to size and laidinto tool 507, either by hand or with fiber placement machine 513.Low-flow composite material 503, if used in the absence of high-flowadhesive 505, could be any composite material that has such a highviscosity so as to possibly produce marcels when subjected to a curingprocess inside a closed cavity tool 507. “Marcels” are wrinkles in thefiber structure of a composite that severely compromise the structuralintegrity of a composite part. Marcels are often created when low-flowcomposite material 503, if used in the absence of high-flow adhesive505, is forced to conform to the inside surface of closed cavity tool507, causing the highly viscous epoxy to flow and distort fibers.Complete curing of the distorted fibers, or marcels, causes the fibersto be permanently fixed in the marcelled state.

The system of the present application seeks to at least prevent theformation of “marcels” by applying layers of uncured low-flow compositematerial 503, as well as a layer of uncured high-flow adhesive 505, in aconfiguration to produce molded rotor yoke 501. In an alternativeembodiment, a plurality of layers of high-flow adhesive 505 may also beused in conjunction with a plurality of layers of low-flow compositematerial 503, to form molded rotor yoke 801 (see FIG. 9). The use ofuncured high-flow adhesive 505 in conjunction with low-flow compositematerial 503 provides a material with low viscous properties that easilybleeds out of tool 507 during curing, thereby preventing low-flowcomposite material 503 from forming marcels. An example of high-flowadhesive 505 is AF163 made by 3M. High-flow adhesive 505 is preferably,in its uncured state, a film, but may also be a paste. High-flowadhesive 505 may also be impregnated with fibers or scrim in order totailor strength and final thickness control.

FIG. 4 depicts molded rotor yoke 501 during the curing process. Closedcavity tool 507 has been compressed in order to rid the part of anyvoids, or air bubbles, and to conform molded rotor yoke 501 to thecontours of two sided tool 507. Mechanical stops 515 a and 515 b ofsecond tool 511 are shown in contact with first tool 509.

Contact between stops 515 a and 515 b, and first tool 509, signify thedesired final thickness of molded rotor yoke 501 has been reached. Bleedouts 519 a and 519 b of high-flow adhesive 505 are caused fromcompression of tool 507. During curing, high-flow adhesive 505 mayeither partially or completely bleed out from molded rotor yokes 501 and801, depending on parameters controlling compression of tool 507.Because high-flow adhesive 505 has a lower viscosity than that oflow-flow composite material 503, high-flow adhesive 505 bleeds out oftool 507 instead of low-flow composite material 503. In someembodiments, the viscosity difference between high-flow adhesive 505 andlow-flow composite material 503 may not be large, which could result inbleed outs 519 a and 519 b being a combination of high-flow adhesive 505and low-flow composite material 503. Curing the uncured molded rotoryoke 501 is accomplished by applying at least one of heat, pressure, andtime. In alternative embodiment, the curing of rotor yoke molded rotoryoke 501 may involve subjecting molded rotor yoke 501 to a vacuum.Another alternative embodiment involves releasably coupling first tool509 and second tool 511, via fasteners 521 a and 521 b, while alloweduncured molded rotor yoke 501 to soak at an ambient temperatureenvironment. The specific amount of variables such as heat, pressure, ortime, depend up on at least the specific curing requirements of thelow-flow composite material 503 and high-flow adhesive 505 used to formmolded rotor yoke 501. The location of bleed outs 519 a and 519 b may belocated anywhere on tool 507 that allows high-flow adhesive 505 toescape or bleed out during the curing process; however, it is preferredthat bleed outs 519 a and 519 b be located on the upper side of tool 507so as to prevent the introduction of air bubbles into molded rotor yoke501.

FIG. 5 depicts molded rotor yoke 501 after the curing cycle has beencompleted. Bleed outs 519 a and 519 b have been removed from moldedrotor yoke 501 by force and then lightly sanded to remove any sharpedges. Layer of high-flow adhesive 505 has decreased in thickness due topartially bleeding out during the curing process.

Referring to FIGS. 6-8 in the drawings, an alternative embodiment of acomposite molded rotor yoke 601 of rotor yoke 901 (shown in FIG. 10) isfabricated by applying a plurality of layers of uncured low-flowcomposite material 503 and a layer of high-flow adhesive 505 into aclosed cavity tool 607. Note that the geometric configuration of tool607 is merely exemplary of the widely diverse geometric configurationsof closed cavity tools contemplated by the present application. Closedcavity tool 607 preferably has a rigid first tool 609 and a rigid secondtool 611. However, closed cavity tool 607 may also have a semi-rigidfirst tool 609, a semi-rigid second tool 611, or any combination ofsemi-rigid and rigid tools 609 and 611. It should be appreciated thattools 609 and 611 may be split into multiple tools. For example, firsttool 609 may be formed as two separate tools. Closed cavity tool 607provides tolerance and contour control by conforming the primarysurfaces of molded rotor yoke 601 to the inside surfaces of closedcavity tool 607. Closed cavity tool 607 may also be referred to as a“two-sided” tool or other language describing that tool 607substantially encloses molded rotor yoke 601.

Uncured, composite molded rotor yoke 601 is formed when the desirednumber of layers, also referred to as “plies”, of low-flow compositematerial 503 and high-flow adhesive 505 have been applied into tool 607,in the desired geometry. Layers of low-flow composite material may belaid by hand, or by fiber placement machine 513. High-flow adhesive 505may also be laid by hand, or by a machine similar to fiber placementmachine 513. Closed cavity tool 607 is capable of compressing moldedrotor yoke 601 into a desired thickness and geometry. Closed cavity tool607 may include stops 615 a and 615 b so that first tool 609 and secondtool 611 of tool 607 will stop the compression of molded rotor yoke 601at the desired thickness of molded rotor yoke 601. It should beappreciated that stops 615 a and 615 b may be alternatively integratedinto second tool 611, or stops 615 a and 615 b may be separate partswhile remaining configured to stop the compression of first tool 609 andsecond tool 611 at the appropriate desired thickness of molded rotoryoke 601.

Uncured low-flow composite material 503 preferably includes glass fibersdisposed in an uncured epoxy, in the form of a prepreg, although thepresent application contemplates other materials for molded rotor yoke601. An example of low-flow composite material 503 is HexPly 8552 madeby Hexcel Composites. For this application, the term “prepreg” istypically sheets of fibers impregnated in uncured epoxy or adhesive.Uncured low-flow composite material 503 can then be cut to size and laidinto tool 607, either by hand or with fiber placement machine 513.Low-flow composite material 503, if used in the absence of high-flowadhesive 505, could be any composite material that has such a highviscosity so as to possibly produce marcels when subjected to a curingprocess inside a closed cavity tool 607. “Marcels” are wrinkles in thefiber structure of a composite that severely compromise the structuralintegrity of a composite part. Marcels are often created when low-flowcomposite material 503, if used in the absence of high-flow adhesive505, is forced to conform to inside surfaces of closed cavity tool 607,causing the highly viscous epoxy to flow and distort fibers. Completecuring of the distorted fibers, or marcels, causes the fibers to bepermanently fixed in the marcelled state.

Closed cavity tool 607 preferably does not have side tools or bleed outportions; instead, tool 607 has space around the periphery of moldedrotor yoke 601 for an absorbent material 606 a and 606 b. Absorbentmaterial 606 a and 606 b functions at least to absorb high-flow adhesive505 as it bleeds outs of molded rotor yoke 601 during the curingprocess, as further explained below. Additionally a vacuum bag 604 isconfigured in order for a vacuum pump 602 to draw a vacuum on moldedrotor yoke 601 during the curing process. The drawing of a vacuum onmolded rotor yoke 601 during the curing process acts to help remove airbubbles from molded rotor yoke 601. Though vacuum bag 604 is shown asencapsulating only molded rotor yoke 601, it should be appreciated thatin some embodiments vacuum bag 604 may also surround either first tool609, second tool 611, or both first tool 609 and second tool 611. Itshould be appreciated that other materials, such as a breather material,may be used in conjunction with vacuum bag 604 in order to draw a vacuumon molded rotor yoke 601.

The system of the present application seeks to at least prevent theformation of “marcels” by applying layers of uncured low-flow compositematerial 503, as well as a layer of uncured high-flow adhesive 505, in aconfiguration to produce molded rotor yoke 601. In an alternativeembodiment, a plurality of layers of high-flow adhesive 505 may also beused in conjunction with a plurality of layers of low-flow compositematerial 503, to form molded rotor yoke 801 (see FIG. 9). The use ofuncured high-flow adhesive 505 in conjunction with low-flow compositematerial 503 provides a material with low viscous properties that easilybleeds out of molded rotor yoke 601 during curing, thereby preventingthe formation of marcels. An example of high-flow adhesive 505 is AF163made by 3M. High-flow adhesive 505 is preferably, in its uncured state,a film, but may also be a paste. High-flow adhesive 505 may also beimpregnated with fibers or scrim in order to tailor strength and finalthickness control.

FIG. 7 depicts molded rotor yoke 601 during the curing process. Closedcavity tool 607 has been compressed in order to rid the part of anyvoids, or air bubbles, and to conform molded rotor yoke 601 to theprimary contours of two sided tool 607. Mechanical stops 615 a and 615 bof first tool 609 are shown in contact with second tool 611. Contactbetween stops 615 a and 615 b, and second tool 611, signify the desiredfinal thickness of molded rotor yoke 601 has been reached. During thisprocess, high-flow adhesive 505 bleeds into absorbent material 606 a and606 b due to compression of tool 607 and the drawing of a vacuum throughvacuum pump 602. During curing, high-flow adhesive 505 may eitherpartially or completely bleed out from molded rotor yokes 601 and 801,depending on the parameters controlling compression of tool 607. Becausehigh-flow adhesive 505 has a lower viscosity than that of low-flowcomposite material 503, high-flow adhesive 505 bleeds out of tool 607instead of low-flow composite material 503. In some embodiments, theviscosity difference between high-flow adhesive 505 and low-flowcomposite material 503 may not be large, which could result in a smallamount of resin from low-flow composite material 503 with the high-flowadhesive 505 bleeding into absorbent material 606 a and 606 b. Curingthe uncured molded rotor yoke 601 is accomplished by applying at leastone of heat, pressure, and time. An alternative embodiment involvesreleasably coupling first tool 609 and second tool 611, via fastenerswhile allowed uncured molded rotor yoke 601 to soak at an ambienttemperature environment. The specific amount of variables such as heat,pressure, or time, depend up on at least the specific curingrequirements of the low-flow composite material 503 and high-flowadhesive 505 used to form molded rotor yoke 601.

FIG. 8 depicts molded rotor yoke 601 after the curing cycle has beencompleted. The layer of high-flow adhesive 505 has decreased inthickness because of adhesive 505 partially bleeding out during thecuring process.

FIG. 9 depicts an alternative embodiment of molded rotor yoke 801 thatwas formed by either the process used to form molded rotor yoke 501 ormolded rotor yoke 601, except that a plurality of layers of high-flowadhesive 505 were used. Multiple layers of high-flow adhesive 505 allowsfor a greater amount of high-flow adhesive 505 available for bleed out.Using a plurality of layers of high-flow adhesive 505 can beadvantageous for many reasons, such as for tailoring the materialproperties of molded rotor yoke 801, as well as for allowing for greatercontour variation in tools 507 and 607.

FIG. 10 depicts a preferred embodiment of a rotorcraft rotor yoke 901.Rotor yoke 901 is preferably made from molded rotor yoke 501, but mayalso be made from molded rotor yoke 601 or 801. Rotor yoke 901exemplifies features that may be machined into molded rotor yokes 501,601, and 801 using a machining tool such as a five-axis machine tool.Such features include: inner openings 905 a , 905 b, and 905 c, outerperiphery 903, rotor blade attachment holes 907 a and 907 b, and mastattachment holes 909 a-909 h, to name a few. Rotor yoke 901 is formedwhen all machining operations are complete. It should be noted that, inone embodiment, molded rotor yoke 501, 601, and 801 are oversized, i.e.,is larger in physical dimensions than rotor yoke 901 to provide materialfor removal during a machining process to form machine outer periphery903 (shown in FIG. 10). Moreover, dimensions of openings 905 a, 905 b,and 905 c maybe incorporated into molded rotor yokes 501, 601, or 801and then increased in size by a subsequent machining operation.

FIG. 11 depicts the preferred embodiment of a rotor hub 1001 comprisinga pair of rotor yokes 901, a coupling 1003 that mechanically couplesrotor yokes 901 to a mast 1005, and fittings 1007 a-1007 d thatmechanically couple rotor yokes 901 to rotor blades 1009 a-1009 d,respectively. The configuration of rotor hub 1001 depicted in FIG. 11 ismerely exemplary of the widely various embodiments of rotor hub 1001contemplated by the present application.

It should be noted, that the methods disclosed in the presentapplication can be applied to form composite structures other than rotoryoke 901 or molded rotor yokes 501, 601, and 801. Any compositestructure that uses low-flow composite material 503 that is susceptibleto marcelling, or other fiber distortion, during compression in a closedcavity tool such as closed cavity tools 507 or 607, would benefit fromthe methods disclosed in the present application. Examples of compositestructures that would fall into this category include, but not limitedto, composite structures used in aircraft, wind turbines, automobiles,marine vehicles, etc.

The system of the present application provides significant advantages,including: (1) ability to use two-side tooling while providing acomposite rotor yoke without marcelling of the reinforcing fibersthereof; (2) enabling the use of toughened, low-flow resins in compositerotor yokes in a closed cavity tool; and (3) providing a composite rotoryoke that requires less composite fabrication time, cost, and effortwith less part-to-part variation than conventional rotor yokes.

The particular embodiments of the system of the present applicationdisclosed may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown, other than as describedin the claims below. It is therefore evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of the presentapplication. Accordingly, the protection sought herein is as set forthin the claims below. It is apparent that a system with significantadvantages has been described and illustrated. Although the system ofthe present application is shown in a limited number of forms, it is notlimited to just these forms, but is amenable to various changes andmodifications without departing from the spirit thereof.

1. A method of making a rotor yoke, comprising: preparing a molded rotoryoke in a closed cavity tool, comprising: applying layers of uncuredlow-flow composite material and a layer of uncured high-flow adhesive ina configuration to produce an uncured molded rotor yoke; substantiallyenclosing the uncured molded rotor yoke in the closed cavity tool,wherein the closed cavity tool comprises a first tool and a second tool;forcing the first tool and the second tool together, so as to compressthe uncured molded rotor yoke; and curing the uncured molded rotor yoke.2. The method according to claim 1, further comprising: machining atleast one portion of the molded rotor yoke to form the rotor yoke. 3.The method according to claim 1, wherein the curing of the uncuredmolded rotor yoke includes applying at least one of heat, pressure, andtime.
 4. The method according to claim 3, wherein the curing of theuncured molded rotor yoke further includes releasably coupling the firsttool and the second tool together while allowing the molded rotor yoketo soak at an ambient temperature environment.
 5. The method accordingto claim 1, wherein the applying of the layers of an uncured low-flowcomposite material and the layer of uncured high-flow adhesive includesan automated fiber placement machine.
 6. The method according to claim1, wherein the forcing of the first tool and the second tool together soas to compress the uncured molded rotor yoke forces at least a portionof the uncured high-flow adhesive to bleed out.
 7. The method accordingto claim 1, wherein the uncured high-flow adhesive is impregnated with aplurality of fibers to provide at least one of strength and finalthickness control.
 8. The method according to claim 1, wherein theuncured low-flow composite material comprises a plurality of glassfibers.
 9. The method according to claim 1, wherein at least one of thefirst tool and the second tool is a rigid structure.
 10. The methodaccording to claim 1, wherein at least one of the first tool and thesecond tool is a semi-rigid structure.
 11. The method according to claim1, wherein the machining of at least one portion of the molded rotoryoke to form the rotor yoke includes machining the cured molded rotoryoke to form mast attachment holes.
 12. The method according to claim 1,wherein the preparing of the molded rotor yoke further comprises:drawing a vacuum in a vacuum bag enclosed around the molded rotor yoke.13. The method according to claim 1, wherein at least one of the firsttool and second tool comprises multiple tools.
 14. The method accordingto claim 1, wherein the closed cavity tool further comprises: at leastone side tool adjacent to a periphery of the molded rotor yoke.
 15. Themethod according to claim 14, wherein at least one of the at least oneside tool, the first tool, and the second tool is a semi-rigid tool. 16.The method according to claim 1, wherein the closed cavity tool furthercomprises at least one tool stop for controlling a thickness of themolded rotor yoke.
 17. The method according to claim 1, wherein thepreparing of the molded rotor yoke further comprises: applying anabsorbent material around a periphery of the uncured molded rotor yokefor absorbing any bleed out of the high-flow adhesive.
 18. A rotor yoke,comprising: layers of low-flow composite material; and at least onelayer of high-flow adhesive applied adjacent to the layers of low-flowcomposite material; wherein the layers of low-flow composite materialand high-flow adhesive having been compressed and cured in a closedcavity tool.
 19. The rotor yoke according to claim 18, wherein thelow-flow composite material comprises glass fibers.
 20. The rotor yokeaccording to claim 18, wherein the high-flow adhesive has a lowerviscosity than the low-flow composite material so as to promote bleedout of the high-flow adhesive during a curing of the rotor yoke, therebypreventing the formation of marcels in the low-flow composite material.